1. Field of the Invention
This invention relates to an electric switch to be used in power systems in excess of 1 kV. More particularly, a radial design increases the exposed electrode surface area by nesting an inner electrode in an outer electrode.
2. Description of the Art
Spark gap switches are used to control the discharge of high voltage energy storage capacitor banks, Marx impulse voltage generators, and other high voltage, high current power systems.
Conventional spark gap switches consist of two or more electrically conducting electrodes separated by a gas-filled region. Spark gap switches are used to hold off voltage until a desired voltage is reached and then the switch breaks down by the formation of an electrically conducting plasma. Conventional spark gap switches are often placed in an insulating housing so as to accommodate different gases and to allow changing the gas density.
Operation of spark gap switches results in erosion of the switch electrodes, thereby increasing the gap length. Electrode erosion is a function of current that has been passed through the electrodes and the length of time the current flows through the electrode. A particular switch configuration typically has an erosion rate measured in micrograms per coulomb of total charge transferred through the switch electrodes. (Total charge transfer is the cumulative time integral of the absolute value of the current passing through the switch.) A typical value for switch erosion is 100 to 200 micrograms per coulomb. In a particular circuit, the breakdown voltage of the switch is usually set by adjusting the pressure (density) of the switch gas dielectric, e.g. air or sulfur hexafluoride (SF.sub.6).
Once the electrodes erode and the gap expands to a certain point, the breakdown voltage can no longer be adjusted to the desired value by changing the density of the switch gas. At that point, the switch is no longer operational.
In the design of a conventional axial-spark switch, insulating material is exposed to debris from sparking, which tends to contaminate the insulating material thereby reducing the operational life of the switch.
U.S. Pat. No. 5,502,346 (Hsieh) discloses an electro-chemical generator to produce, for example, ozone. This apparatus uses an insulating tube inserted into a ground electrode tube.
U.S. Pat. No. 4,126,808 (Rich) discloses a high voltage two stage triggered vacuum gap with high voltage terminals at opposite ends of an envelope. Vacuum switches use plasma generators to inject plasma into the switch gap.
U.S. Pat. No. 3,996,438 (Kurtz) discloses a vacuum-type circuit interrupter with two pluralities of rod electrodes in which the first plurality of electrodes interleave with the second plurality of electrodes.
U.S. Pat. No. 3,854,068 (Rich) discloses a shield structure for vacuum arc discharge devices.
The Rich and Kurtz patents listed above are incorporated by reference in their entirety.
As can be seen from the present state of the art, there exists a need for a switch that can operate at voltages in excess of 1 kV where the switch operational lifetime exceeds a total charge transfer of one million Coulombs, particularly for continuous repetitive operation.